To determine the efficacy of three treatment protocols for pneumocystis carinii in AIDS: 1) Aerosolized pentamidine vs parenteral or oral trimethoprim/sulfamethoxazole 2) A double-blind trial of trimetrexate with leucovorin calcium rescue vs trimethoprim/sulfamethoxazole 3) An open, prospective study of trimetrexate with leucovorin rescue.